1. Field of the Invention
The present invention relates generally to a drawing apparatus and a drawing method of drawing an image on a plate mounted on an outer peripheral surface of a drum.
2. Description of the Background Art
Drawing apparatuses for drawing an image upon irradiation of a plate used for printing with light have been used. In a drum-type drawing apparatus, a plate is mounted on a recording drum which is rotatable in a primary scanning direction, and a recording head comprising a laser diode and the like is moved in a secondary scanning direction parallel to a rotary shaft of the recording drum, to draw an image on the plate.
FIG. 9 is a schematic perspective view of a recording drum in a conventional drawing apparatus. A plate 160 made of aluminum serving as a recording material is mounted on a recording drum 150 shown in FIG. 9. A front end clamp 170 for fixing one end of the plate 160 and a rear end clamp 180 for fixing the other end of the plate 160 are mounted on an outer peripheral surface of the recording drum 150. The rear end clamp 180 contains a magnet, and is fixed by a magnetic force to a position, on the outer peripheral surface of the recording drum 150, corresponding to the size of the plate 160.
The recording drum 150 having the plate 160 attached thereto is rotated at relatively low speed around a rotary shaft 190, so that an image is drawn on the surface of the plate 160.
In the conventional drawing apparatus, positioning pins (not shown) for positioning the plate 160 are provided on the outer peripheral surface of the recording drum 150. Positioning holes for a recording drum (hereinafter referred to as recording drum positioning holes) to be respectively fitted on the positioning pins are formed at one end of the plate 160. In mounting the plate 160 on the recording drum 150, the recording drum positioning holes of the plate 160 are respectively fitted on the positioning pins of the recording drum 150. Accordingly, it is possible to accurately position the plate 160 on the outer peripheral surface of the recording drum 150.
On the other hand, positioning pins for positioning the plate 160 are also provided on the body of a printing machine. The positions of the positioning pins differ depending on the specification of the printing machine. Therefore, in the plate 160, positioning holes for a printing machine (hereinafter referred to as printing machine positioning holes) must be respectively formed in positions corresponding to the specification of the printing machine.
Generally after the image is drawn on the plate 160 by the drawing apparatus, the printing machine positioning holes are respectively formed in predetermined positions of the plate 160 on the basis of an end surface of the plate 160 using a punching machine. The plate 160 can be positioned on the body of the printing machine by respectively fitting the printing machine positioning holes formed in the plate 160 on the positioning pins of the printing machine.
However, the size of the plate 160 varies. When the printing machine positioning holes are formed on the basis of the end surface of the plate 160 after the image is drawn by the drawing apparatus, the relationship between the image formed on the plate 160 and the printing machine positioning holes varies. In this case, the shift in the position for printing must be corrected by shifting the plate 160 mounted on the body of the printing machine while seeing the results of the printing obtained by the printing machine using the plate 160. Therefore, printing work becomes complicated.